It is well known, particularly in the field of transporting and using particulate materials, commonly powders, granules, pellets, and the like, that it is important to keep product particles as free as possible of contaminants. Particulates are usually transported within a facility where they are to be mixed, packaged or used in a pressurized tubular system that in reality produces a stream of material that behaves somewhat like a fluid. As these materials move through the pipes, considerable friction is generated not only among the particles themselves, but also between the tube walls and the particles in the stream. In turn, this friction results in the development of particle dust, broken particles, fluff, streamers (ribbon-like elements that can “grow” into quite long and tangled), glass fibers in glass filled products, that can impede the flow of materials. The characteristics of such a transport system are quite well known, as is the importance and value of keeping product particles as free as possible of contaminants.
The term “contaminant” as used herein includes a broad range of foreign material and includes foreign material as well as broken particles or streamers of the product being transported. The generation of contaminants, also referred to as dust, including microdust, can be from a large number of sources, including, in the way of examples, the creation of dust particles during the processing of plastic pellets in which the larger particles are segregated to be re-ground; organic matter in food grains, such as shells and hulls; the creation of dust in the formation of iron ore pellets; and, as noted previously, the mere conveyance of the pellets in pipes and other mechanical conveying and handling systems. Using plastics as an example, such foreign material could have a detrimental effect on the finished product. Specifically, foreign material different in composition from the primary material, such as dust, and non uniform material of the primary product, such as streamers, would not necessarily have the same melting temperatures as the primary product and would cause flaws when the plastics material is melted and molded. Furthermore, streamers can impact the weighing scale and plug the dosing screws at bagging stations.
Considering product quality, and focusing on moldable plastics as a primary example, foreign material different in composition from the primary material, such as dust, non-uniform material of the primary product, fluff, and streamers, does not necessarily have the same melting temperatures as the primary product and causes flaws when the material is melted and molded. These flaws result in finished products that are not uniform in color, may contain bubbles, and often appear to be blemished or stained, and are, therefore, unsellable. It is important to note that since these same non-uniform materials often do not melt at the same temperature as the primary product, the unmelted contaminants cause friction and premature wear to the molding machines, resulting in downtime, lost production, reduced productivity, increased maintenance and thus increased overall production costs.
Since dust and other contaminants are generated mostly by the transport system, it is of primary importance to not only provide apparatus for thoroughly cleaning the particles, but to do so as close to the point of use of the particles as possible so as to avoid the generation of contaminants through additional transport. Accordingly, compact dedusters have been used for many years to clean materials in this application, capable of handling smaller volumes of product, yet also capable of thoroughly cleaning the product. The compact dedusters permit the installation of the deduster immediately before final use of the products, such as being installed directly on top of molding machines or extruders, or on top of silos, as well as under silos, before packaging and bagging, rather than at an earlier stage after which re-contamination can occur before the products are utilized. Of course, the dedusters can be installed as a free standing unit, as well.
Dedusters used to clean contaminants from particulate material can be found in U.S. Pat. No. 5,035,331, granted to Jerome I. Paulson on Jul. 30, 1991, in which air is blown upwardly through wash decks over which a flow of contaminated particulate material is passed so that the flow of air up through the wash decks removes the contaminants from the material flow. A magnetic field is provided by the deduster so that the particulate material flow passes through the magnetic field to neutralize the static charge on the particulates and facilitate the removal of the contaminants from the material. The flow of contaminant laden air is discharged from the deduster, while the cleaned particulate material is passed on to the manufacturing process.
A compact dedusting apparatus is disclosed in U.S. Pat. No. 6,595,369, granted on Jul. 22, 2003, to Jerome I. Paulson. Like the larger dedusting apparatus depicted in U.S. Pat. No. 5,035,331, the follow of particulate material is cleansed of contaminates that have had the static charged attracting the contaminates to the particulates neutralized. The cleaning process utilizes a flow of air passing through the stream of particulate material passing over wash decks. The contaminate-laden air is discharged through the top of the dedusting apparatus, while the cleaned particulate material is discharged from the bottom of the deduster.
In U.S. Pat. No. 7,380,670, granted on Jun. 3, 2008, to Jerome I. Paulson, et al, and in U.S. Pat. No. 8,016,116, granted on Sep. 13, 2011, to Heinz Schneider, the dedusting apparatus includes a pair of oppositely directed wash decks receiving contaminated particulate material from a common infeed port. The infeed mechanism divides the material flow between the two opposing wash decks and directs the particulate material over a flow of air passing through the first wash decks, then through laterally spaced Venturi zones and onto inwardly directed secondary wash decks that direct the cleaned particulate material into a central discharge opening. Air flow to the primary and secondary wash decks is directed through a rearwardly located manifold that has a central primary opening and laterally spaced lower openings below the secondary wash decks.
These compact dedusters are provided with single, offset and double (back-to-back) wash decks and are utilized with a vertically oriented conduit in which particulate material is conveyed to the manufacturing apparatus utilizing the particulate material. Accordingly, the product inlet opening at the top of the dedusting apparatus is in vertical alignment with the cleaned product outlet opening. The particulate material is introduced into the inlet opening and is metered onto a diagonally oriented primary wash deck through which air is blown from an air supply inlet to clean dust and debris from the particulate material flowing over the wash deck. In these dedusting devices, the particulate material is discharged off the lower end of the wash deck and falls through a Venturi zone in which air is moving upwardly to provide a vigorous cleaning action to the particulate material. The material falling through the Venturi zone is received on a secondary wash deck that is oriented oppositely of the primary wash deck to direct material back to the centrally aligned cleaned product outlet opening.
With increasing capacity of the dedusting apparatus, it would be advantageous to provide for a fully balanced distribution of the inflow of particulate material to be cleaned over the opposing wash decks of the dedusting apparatus, or in the offset dedusting apparatus, an even flow over the full width of the wash deck. In conventional dedusting devices, the flow of particulate material onto the wash decks typically passes through a rotary valve and then through a circular inlet opening onto rectangular wash decks. As a result, even flow over the full width of the wash decks is not usually accomplished.
It would be advantageous to provide a configuration for a dedusting apparatus that enables a uniform distribution of the particulate material to be cleaned over the full width of the wash decks. It would also be advantageous to be able to terminate selectively the flow of particulate material over the wash decks. In addition, it would be advantageous to provide a configuration for a dedusting apparatus that enables the rotary valve to be eliminated from the overall combination of components while passing the infeed of particulate materials through a circular infeed opening.